Subdural Hygroma versus Atrophy on MR Brain Scans:
"The Cortical Vein Sign"
Kerry W . McCiuney, 1 Joel W . Yeakley , 1 Marc J . Fenstermacher, 1 Samuel H. Baird , 1 and Carmen M. Bonmati 1
PURPOSE: To determine if the position of the superficial cerebral cortical veins can be used to
distinguish subdural hygroma from atrophy on MR brain scans. METHODS: Retrospective review
of MR scans obtained in cases of extracerebral fluid collections, separating these into two groups,
ie, subdural hygroma or atrophy. FINDINGS: All cases of atrophy in this study showed cortical
veins and their branches traversing widened cerebrospinal fluid spaces over the cerebral convexities. None of the subdural hygroma patients showed this finding . Cortical veins in hygroma patients
were seen only at the margin of the displaced cortex, and did not traverse t he fluid collections
over the cerebral convexities. CONCLUSIONS: The authors call the visualization of cortical veins
and their branches within fluid collections at the cerebral convexities "the cortical vein sign. " They
believe this sign to be prima facie evidence of atrophy; its presence rules out the diagnosis of
subdural hygroma in the region of interest.
Index terms: Cerebral hematoma, magnetic resonance; Cerebral atrophy, magnetic resonance;
Veins, cerebral
AJNR 13:1335-1339, Sep/ Oct 1992
Distinguishing between subdural hematoma
and subdural hygroma by magnetic resonance
(MR) imaging is usually not a problem since
subdural hematomas usually contain blood products that alter the signal characteristics of the
extracerebral fluid collection sufficiently that it
may be recognized as different from cerebrospinal
fluid (CSF) (1-4). This is true even in subdural
hematomas of various ages that may be isodense
to brain or CSF by computed tomography (CT)
(2). However, when an extracerebral fluid collection is isodense to CSF on CT, various criteria
have been utilized for predicting whether it represents the results of widening of the subarachnoid space due to atrophy versus a subdural fluid
collection. These criteria usually are based on
"mass effect" on the brain such as flattening of
the cortical surface with obliteration of sulci with
subdural hygroma, as opposed to abnormal
prominence of the cortical sulci with atrophy.
Received May 2, 1990; revision req uested June 5 and received July
25, 1991; final acceptance on November 18.
1
Department of Radiology , The University of T exas Hea lth Science
Center, 6431 Fannin Street, Houston, T X 77030. Address reprint requests
to Joel W. Yeakley, MD.
AJNR 13:1335-1339, Sep/ Oct 1992 0195-6108/ 92/ 1305-1335
© American Society of Neuroradiology
These observations may be very subjective and
inconclusive in many cases. The same difficulty
arises on MR images when the extracerebral fluid
collection is isointense to spinal fluid on all pulse
sequences. This could occur in true "hygromas"
that are the result of arachnoid tear or insufficiency allowing spinal fluid to enter the subdural
space, or, theoretically, in subdural hematomas
of sufficient age that blood products or their
proteinaceous residual are not present in amounts
adequate to allow differentiation of hygroma versus atrophy on the basis of differences in signal
intensity.
We describe a method of distinguishing between subdural hygroma and atrophy that depends on objective observation of whether the
cortical veins cross the fluid collection over the
convexities at some distance from the sagittal
sinus (atrophy) versus whether the cortical veins
reach the brain surface immediately adjacent to
the sagittal sinus and are not seen crossing the
fluid collection over the convexities (hygroma).
We refer to the visualization of the cortical
veins within the widened CSF spaces over the
cerebral convexities in cases of atrophy as the
"cortical vein sign" and we have developed a
theoretical model to explain the basis of the sign
1335
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McCLUNEY
AJNR: 13, September /October 1992
+-PIA
RETRACTED CORTEX
N ,4U"AAPHY
Fig. 1. Theoretical model showing the basis of the cortical vein sign. The cortical veins and their branches are tubular structures
draining into the sagittal sinus (black bordered inverted triangle). Notice that with subdural hygroma the arachnoid membrane has
carried all venous structures below it onto the cortical surface of the brain, closing the subarachnoid space. The converse is true in
atrophy. The arachnoid membrane remains closely applied to the dura on the "anticortical" (calvarial) surface of the CSF collection until
the arachnoid is penetrated, opening the subarachnoid space. Veins course normally through the widened subarachnoid space in atrophy
(double-headed arrows). In subdural hematoma, the position of the veins may be similar to that in subdural hygroma or may be ruptured
as shown.
(Fig. 1). The purpose of this retrospective study
was to verify our conclusion drawn from the
model, namely, that the cortical vein sign is
specific for atrophy and excludes a diagnosis of
subdural hygroma.
Materials and Methods
We retrospectively reviewed MR scans of patients with
extracerebral fluid collections isointense to CSF utilizing
standard radiographic criteria to separate these into two
groups, ie, subdural hygroma or atrophy. We accumulated
cases until a total of 10 cases in each group was achieved .
Criteria for inclusion in the subdural hygroma group were
as follows (5, 6) : 1) isointense semilunar or crescent shaped
extracerebral fluid collection limited to a cerebral convexity;
2) mass effect manifested by flattening of cortical surface
of the brain and relative lack of visualization of cortical
sulcal spaces adjacent to the fluid collection; 3) unilaterality
where applicable; and 4) ventricular compression.
Criteria for inclusion in the atrophy group were as follows
(7, 8) : 1) symmetrical enlargement of ventricles, basal
cisternal spaces, and cortical sulcal spaces; and 2) lack of
mass effect on the brain adjacent to the fluid collection.
We purposely eliminated historical data such as history
of trauma or dementia, or the age of the patent, as criteria
in an effort to be more objective on the basis of radiologic
criteria alone.
W e realize that this selection process is imperfect because of the fact that the diagnoses were not generally
confirmed by surgery or autopsy in our series.
The relative location of where the cortical veins cross
the fluid collection was reviewed in each case. That is, we
analyzed whether the veins randomly crossed the CSF
space even over the convexities and then followed a juxtacortical location, or whether the veins crossed the fluid
collection in an immediate parasagittal location and assumed a juxtacortical location lateral to that point. In the
latter group, the veins were not seen crossing the fluid
space over the convexities.
Several additional cases of subdural hematoma at various stages of blood product degradation were reviewed to
confirm the inwardly displaced cortical veins over the
convexities in that condition previously described by Fobben et al (4).
The majority of the examinations were performed on a
1.5-T Signa scanner (GE, Milwaukee, WI) utilizing the
standard head coil. Sagittal T1-weighted spin-echo images
(800/20/1) and axial proton-density and T2-weighted images (2000/20,80/1) were utilized. Other parameters included 24.0-cm field of view , 5-mm section thickness with
2.5-mm gap, and 256 X 192 matrix. One scan performed
outside this institution on a Picker 0.5-T scanner is also
included in the illustrations.
Results
All cases of cerebral atrophy showed cortical
veins or their branches within widened CSF-filled
subarachnoid spaces over the hemispheric convexities (Fig. 2). These veins were noted at several
AJNR : 13, September / October 1992
CORTICAL VEIN SIGN
locations within the widened CSF spaces. Many
of these veins appeared to be on a long traverse
across the CSF space (Fig. 3) while others appeared to be "floating" or partially retracted from
their normal sulcal positions. In particular, veins
were frequently demonstrated on the "anticortical" (calvarial) surface of the widened CSF spaces
on sagittal T1-weighted images. These "anticortical" veins lie at a constant depth and are presumably located within CSF just beneath the arachnoid membrane (Fig. 4).
All cases of subdural hygroma showed the fluid
collections over the convexities to be void of
vascular structures. Cortical veins in these cases
could be seen only at the margins of the displaced
cortex (Figs. 5 and 6).
All the cases of subdural hematoma with signal
intensities different than that of CSF showed a
location of the cortical veins in a similar location
to the subdural hygromas, and none showed
cortical veins randomly traversing the fluid collections over the convexities.
1337
Discussion
On the convexities of the normal brain, the
superficial cortical veins lie within the cortical
sulci in close approximation to the underlying pia
and the overlying arachnoid/ dura membranes.
These veins drain by branches that must first
penetrate the overlying arachnoid and then the
inner layer of the dura to reach a dural venous
sinus. In the case of the cerebral convexity veins,
this is the superior sagittal sinus (9).
To determine whether the position of the superficial cortical veins could be used to distinguish
subdural hygroma from atrophy, the literature
was reviewed and a theoretical model was developed (Fig. 1).
The model was based on the following lines of
reasoning:
1. In cerebral atrophy, the brain cortex gradually recedes from the arachnoid/ dura membranes. Since the arachnoid remains closely applied to the dura, recession of the cortex results
in widening of the subarachnoid space (10). This
space, however, retains its normal complement
of cortical veins and branches. There is probably
some "tethering" of these veins by their downstream arachnoid penetrations and dural attachments, near the sagittal sinus. Otherwise, the
veins are obliged to continue to traverse the everwidening subarachnoid space as the cortex recedes. These venous structures are, in fact , ubiquitous in the subarachnoid space and are easily
visible on MR scans as "flow voids" or areas of
high signal intensity depending upon the venous
flow rate and the parameters used (11) (Figs. 24).
Fig. 2. A T1-weighted , off midline, sagittal view , 800/ 20/ 1
(TR/ TE/ excitations), in a patient with atrophy . Notice that some
of the veins (curved arrows), which are seen as rounded "flow
voids" in the CSF, lie some distance from the cortical surface of
the brain.
2. In the presence of subdural hygroma or
hematoma, the subdural space is expanded by
fluid between the dura and the arachnoid, forcing
the arachnoid membrane against the cerebral
cortex (4, 12, 13). This relatively closes the subFig. 3. A T1-weighted , off midline, sagittal view (800/ 20) showing a vein on a long
"transverse" (arrow) across the widened CSF
space in thi s patient with atrophy.
Fig. 4. A T1-weighted, off midline, sagittal view (800/ 20) in another patient with
atrophy . Notice the veins (open arrows) seen
as rounded "flow voids. " The middle arrow
points to a vein on the "anticortical'" (calvarial) surface of the widened CSF space. Th1s
vein is probably located within CSF just
beneath the arachnoid membrane , a position
it could not occupy if a subdural hygroma
were present in the region .
3
4
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AJNR: 13, September / October 1992
McCLUN EY
Fi g. 5. A, Tl -weighted, off midline sagittal view (800/20) in a patient with subdural
hygroma. Unli ke atrophy, the corti ca l veins
are not seen crossing the fluid collection bu t
are identified onl y on the displaced brain
surface (arrows). Note post-traumatic skull
defect with bra in herniation.
B, Confirmation of findings on Tl weighted coronal view (800/20).
A
arachnoid space, trapping the cortical veins
within it and displacing the arachnoid membrane
and cerebral cortex as a unit away from the
overlying dura. This leaves a homogenous fluid
collection between the dura and arachnoid that is
void of visible vascular structures (Figs. 5 and 6).
The cortical veins that are visualized following
the cortical surface of the brain at the cerebral
convexities (Figs. 5 and 6) still have to reach the
sagittal sinus, but they do so only far medially in
the parasagittal area as may be observed on the
venous phase of arteriograms with subdural fluid
collections of any type (13). In addition, in sub-
Fig. 6. Chronic subdural fluid collection (hygrom a) isointense
to CSF . This axial T 2-weighted scan (2000/ 80) dem onstrates that
the extracerebral fluid co llection on the ri ght is void of vi sible
vascular structures and that the corti ca l veins (curved arrows)
can be seen only at the cortical m argins.
B
dural hematoma, but not usually in subdural
hygroma, some of bridging veins may be ruptured as they pass from the brain surface to the
sagittal sinus, further contributing to the relative
lack of venous structures within fluid collections
over the convexities.
Following the development of the theoretical
model, our study was conducted comparing MR
brain scans of patients with subdural hygroma to
those with atrophy. All subdural hygromas were
free of venous structures within the fluid collections over the convexities and all cases of atrophy
showed venous structures within the overlying
CSF fluid collections. Of particular interest was
the finding of collections of veins on the "anticortical" (calvarial) surface of the fluid collections
in patients with atrophy. These were best seen
on T1-weighted sagittal images near the sagittal
sinus (Fig. 4). These veins probably lie within CSF
just beneath the arachnoid membrane.
It is to be noted that subdural fluid collections
isointense to extraventricular CSF are uncommon. Chronic subdural hematomas usually have
a significantly greater protein content than extraventricular CSF and are easily distinguished on
MR due to their T1-shortening effect (1-4, 14).
However, subdural hygromas that are generally
isointense to extraventricular CSF can present
diagnostic difficulties. Hygromas may be the result of tears, or insufficiency, in the arachnoid
membrane that allow CSF to enter the subdural
space producing an extracerebral fluid collection
with signal intensities identical to CSF on all
imaging parameters. A subdural hematoma of
sufficient age that products of blood degradation
AJNR : 13, September /October 1992
are no longer present could theoretically produce
a similar appearance.
Morphologically , the recognition of veins along
the margin of the displaced cortex in extracerebral fluid collections is a valuable sign long known
to angiographers (13) and reported by others (4).
However, the true significance of this sign is that
the veins are seen only at the cortical margins in
extracerebral fluid collections (Figs. 5 and 6). In
atrophy, they are not only at the margins but
also within the fluid and at the anticortical surface
of the fluid.
CORTICAL VEIN SIGN
1339
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Conclusion
The conclusion to be drawn from the model
and this study is that, if cortical veins can be
demonstrated deep within a convexity fluid collection , then that fluid must be CSF within dilated
subarachnoid spaces and not subdural hygroma.
We have called the visualization of cortical
veins and their branches deep within low signal
intensity convexity fluid collections "the cortical
vein sign." We believe this sign to be prima facie
evidence of atrophy and that the sign excludes
the diagnosis of subdural hygroma in the region
of interest.
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Acknowledgments
13. Ramsey
We credit Margaret Young for the physical production
of the manuscript. Jay Johnson for the illustrations, and
Juan Cabrera (posthumously) and Bob Boeye for Figure 1.
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